The flexible pipes for offshore use are often unbounded pipes. The term “unbounded” means in this text that at least two of the layers of the pipe are not bonded to each other. Often unbounded flexible pipes comprise an internal sheath which forms a barrier against the outflow of the fluid which is conveyed through the pipe, and one or more armouring layers on the outer side of the internal sheath (outer armouring layer(s)). The flexible pipe may comprise additional layers such as a carcass which is an inner armouring layer to prevent the collapse of the internal sheath. An outer sheath may be provided with the object of forming a barrier against the ingress of fluids from the pipe surroundings to the armouring layers. In practice the pipe will normally comprise at least two armouring layers, which are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.
The above-mentioned type of flexible pipes is used, among other things, for off-shore as well as some on-shore applications for the transport of fluids and gases. Flexible pipes can e.g. be used for the transportation of fluids where very high or varying water pressures exist along the longitudinal axis of the pipe, such as riser pipes which extend from the seabed up to an installation on or near the surface of the sea, pipes for transportation of liquid and gases between installations, pipes which are located at great depths on the seabed, or between installations near the surface of the sea.
An umbilical is a type of flexible pipe which is used for the transport of process liquids and hydraulic oil and for carrying light and power from an installation positioned at the surface of the sea and down to the oil wells on the seabed. Umbilicals are not directly involved in the transport of oil and gas, but may be necessary for the supply of the process liquids which, as mentioned, are to be used for the recovery of oil, as well as for the running of hydraulic pipes, electrical wires, fibre optics, etc. An umbilical may be combined with an oil/gas transporting pipe e.g. a riser to form an integrated production umbilical or an integrated service umbilical.
Often it is desired to measure one or more chemical, physical and/or mechanical actions to which the flexible pipe is exposed during use.
Sensors for measuring chemical, physical and/or mechanical actions are well known in the art. Sensors of the strain gauge type are frequently used for measuring forces that cause mechanical deformations, in which strain gauges the electrical resistance in a conductor is changed by a mechanical impact. Moreover, sensors monitoring changes in the properties of an optical component caused by mechanical deformations or temperature variations are known.
Sensors and possible transmission lines of sensors will hereinafter be referred to as sensor arrangements.
Clearly, the use of sensor arrangements of the above-mentioned type for monitoring flexible pipes requires that they be mounted well-protected so that they are not damaged in use.
In connection with flexible pipes where the structure of the pipes is of the so-called unbonded type, i.e. the structure comprises several layers and the layers must be capable of moving relative to each other in order for the pipe to remain flexible. Therefore, if the sensor arrangement was disposed freely between the layers, it would quickly be damaged.
Applicant has earlier provided a method of mounting such sensor arrangement in an armouring layer by providing a groove in an armouring wire and fixing the sensor arrangement in this groove with a glue and/or by mechanical deformation of the groove. This method is disclosed in U.S. Pat. No. 7,024,941.
The object of the invention is to provide an alternative flexible pipe with integrated sensor arrangement. The invention also relates to a method of mounting a sensor arrangement in a flexible pipe, ensuring that the sensor arrangement is well protected against undesirable mechanical impacts and is thus operationally reliable during the service life of the flexible pipe.
This object has been achieved by the invention as claimed.